1. Field of the Invention
The present invention generally relates to a magnetic disk device, and more particularly to a magnetic disk device which performs recording/reproducing processing to a magnetic disk by driving an actuator on which a magnetic head is provided, by using a magnetic circuit attached to a base.
2. Description of the Related Art
FIG. 1 through FIG. 4 are diagrams for explaining the composition of a conventional magnetic head device 100.
FIG. 1 is a perspective view showing the conventional magnetic disk device 100, and FIG. 2 is a cross-sectional view of the magnetic disk device 100 taken along the line X1-X1 indicated in FIG. 1. FIG. 3 is a perspective view showing the mounting structure of a magnetic circuit 150 (described later) in the magnetic disk device 100, and FIG. 4 is an enlarged cross-sectional view showing the neighborhood portion of a screw 126 in the state where the magnetic circuit 150 is fixed to the base 113.
As shown in FIG. 1 through FIG. 4, the actuator 122 supports the head slider 114 on which a magnetic head is mounted, and the actuator 122 is supported on the shaft 140 such that the actuator 122 can be swung around the shaft 140. The voice coil 151 is mounted at the rear-end part of the actuator 122 behind the shaft 140.
The voice coil 151 is driven by the magnetic circuit 150 so that the actuator 122 is swung around the center of the shaft 140.
The magnetic circuit 150 is constituted by the upper yoke 153A, the lower yoke 153B, the upper magnet 155A, and the lower magnet 155B. As shown in FIG. 2 and FIG. 3, the upper magnet 155A is disposed on the bottom surface of the upper yoke 153A, and the lower Magnet 155B is disposed on the top surface of the lower yoke 153B.
A gap is formed between the upper magnet 155A and the lower magnet 155B, and the voice coil 151 of the actuator 122 is movably disposed in this gap.
The voice coil 151, the upper yoke 153A, the lower yoke 153B, the upper magnet 155A, and the lower magnet 155B constitute the voice coil motor 123 (VCM). This voice coil motor 123 serves as a source of a drive which swings the actuator 122 around the center of the shaft 140.
In the following explanation, it is supposed that the upper and lower yokes 153A and 153B and the upper and lower magnets 155A and 155B, excluding the voice coil 151, among the components of the voice coil motor 123, constitute a magnet circuit 150, and these are called the components of the magnetic circuit 150.
In the magnetic disk device 100, it is necessary to position the head slider 114 (magnetic head) at a given location on the magnetic disk 101 with high precision, in order to perform proper magnetic recording/reproducing processing.
For this reason, the actuator 122 and the shaft 140 which supports the actuator 122 are disposed on the base 113 with high precision. Under the present circumstances, in order to keep an appropriate state of the head slider 114 (magnetic head) and the magnetic disk 101 at the time of recording/reproducing, accurate positioning of the actuator 122 and the shaft 140 in the height direction on the base 113 is important.
Moreover, the voice coil 151 of the actuator 122 which is disposed with high precision is inserted in the magnetic circuit 150, and it is also necessary to raise the accuracy of positioning of the magnetic circuit 150 in the height direction on the base 113.
For this reason, as shown in FIG. 3, a reference-height projection 124 is formed in the bottom plate 113A of the base 113, and the magnetic circuit 150 is placed on this reference-height projection 124, so that the height arrangement of the magnetic circuit 150 on the base 113 is thereby determined.
The reference-height projection 124 is formed with high precision, and placing the magnetic circuit 150 on the reference-height projection 124 enables good height accuracy to be attained.
Moreover, the magnetic circuit 150 is provide with washer parts 150, and each washer part 150 has a through hole which passes through the screw 126 being inserted. Therefore, the magnetic circuit 150 is fixed to the base 113 by inserting the screws 126 in the through holes of the washer parts 156 and fastening them to the threaded-hole parts 125.
Moreover, the magnetic circuit 150 is provided with washer parts 156, and each washer part 156 has a through hole which passes through the screw 126 being inserted. Therefore, the magnetic circuit 150 is fixed to the base 113 by inserting the screws 126 in the through holes of the washer parts 156 and fastening them to the threaded-hole parts 125.
As described above, if the height accuracy of the actuator 122 and the magnetic circuit 150 on the base 113 is kept good, it is possible to maintain an appropriate state of the head slider 114 (magnetic head) and the magnetic disk 101 at the time of recording/reproducing.
In order to maintain an appropriate state of the head slider 114 (magnetic head) and the magnetic disk 101, it is necessary to ensure that dust (contamination) may not enter the magnetic disk device 100. If dust enters the space between the magnetic disk 101 and the head slider 114, there is a possibility that the magnetic surface formed in the surface of the magnetic disk 101, and the sliding-contact surface of the magnetic head may be damaged (head crash).
To obviate the problem, various countermeasures for preventing occurrence of dust have been proposed conventionally. For example, see Japanese Laid-Open Patent Application No. 2004-296011.
By the way, when the mounting structure in which the magnetic circuit 150 is placed on the reference-height projection 124 is used to raise the height accuracy of the mounting structure as mentioned above, it is difficult to firmly fix the magnetic circuit 150 to the threaded-hole parts 125. In other words, if the magnetic circuit 150 is firmly fixed to the threaded-hole parts 125, the reference-height projection 124 is crushed and the height accuracy will deteriorate.
For this reason, it is necessary to provide a design gap between the upper surface of the threaded-hole part 125 and the washer part 156 in the state where the magnetic circuit 150 is attached to the base 113 as shown in FIG. 4. In FIG. 4, ΔH indicates this gap.
However, because of the use of the gap ΔH, there is a possibility that the threaded-hole part 125 remains exposed to the inside of the magnetic disk device, which causes occurrence of dust (contamination).
When the screws 126 are fastened to the threaded-hole parts 125, or when the screws 126 are removed from the threaded-hole parts 125, a possibility that dust from the threaded-hole parts 125 may be scattered inside the magnetic disk device 100 becomes high. Thus, if dust (contamination) from the threaded-hole parts 125 is scattered inside the magnetic disk device 100, such dust may cause a head crash to take place as described above.